This invention relates to catalyst systems and processes for hydrotreating hydrocarbons by contacting the hydrocarbon with hydrogen in the presence of an appropriate catalyst. An aspect of hydrotreating which is of particular interest in this invention is denitrification in connection with hydrocracking.
Denitrification of hydrocarbon streams in petroleum refining is particularly important relative to hydrocracking in order to lower the nitrogen content of the feed stream to an acceptable level before subjecting the hydrocarbon feed stream to the complete hydrocracking process. In general, it is desirable to reduce the nitrogen content of the hydrocarbon feed stream to less than 10 parts per million by weight (ppm), preferably less than about 2 ppm and in many cases for increased catalyst life it is important to have the nitrogen content reduced to a level of less than 0.5 ppm.
Hydrodenitrification catalysts which have been used have various disadvantages, which include a tendency to foul with coke or other contamination at an excessive rate, which results in shorter catalyst life than is desired. As the catalyst fouls or deactivates, the denitrification process temperature must be increased to maintain activity. When the maximum temperature allowed by process and equipment limitations is reached, the catalyst must be replaced or regenerated.
Hydrotreating catalysts of various compositions are known in the art. For example, nickel-molybdneum and similar catalysts are disclosed in U.S. Pat. No. 4,210,521; U.S. Pat. No. 4,363,719; U.S. Pat. No. 4,534,852 and U.K. Application No. 2,073,770, the disclosures of which are incorporated herein by reference. However, none of these prior disclosures addresses the problems of catalyst activity and catalyst life in a way which is relevant to the present invention.
It is the object of this invention to provide a denitrification catalyst system which has increased activity, increased operating life and thereby improved economics for hydrotreating processes. The increased life of the denitrification catalysts is desirably provided by reducing the tendency for coking and improving the tolerance of the catalysts for poisons as well as improving the diffusion of hydrocarbons in the catalysts. Other objects of this invention will be apparent from the description herein.